Brush-type-scrubbing systems and appliances are commercially available and are often used for surface maintenance, typically for floor surfaces. However, in some high demand or difficult surface maintenance applications and environments, brush-type-scrubbing systems may be inadequate. Examples of high demand or difficult cleaning applications, particularly those with irregular surfaces or those that must be made particularly clean, include parking garages, gas stations, airport runways and aircraft carrier decks, among others.
These high-demand applications are well served by pressure washers or water blasting or washing systems. These are well known, and are commercially available from many manufacturers.
Schematically, a pressure washer system typically consists of a high-pressure pump system that delivers a cleaning solution to the surface to be cleaned, and a vacuum system that removes the cleaning solution along with debris cleaned from the surface. In addition, the washer system either employs large tanks for the cleaning solution or a recovery system that recycles the cleaning solution.
The input to the recovery system is a combination of cleaning liquid, solid particles, and air. The liquid is returned to the cleaning solution tank, the solids are filtered out and disposed of (usually after passage through the demister), and the air is vented out of the system. The process of separating the air from liquid is called demisting.
A well-known category of demister called a “cyclone separator”, or hydrocyclone, uses centripetal acceleration to separate the air from the liquid and solids. The cyclone separator is based on the same principle as a centrifuge—a mixture of materials is spun, and the materials separate according to their densities. In a cyclone separator, a stream consisting of a combination of liquid, solid particles and air is injected into a roughly cylindrical or conical container along a direction tangent to the inner container wall, so that the stream traces out a roughly circular path along the interior wall of the container. Because the stream moves along a curved path, it is subject to a centripetal acceleration, equal to the velocity squared divided by the radius of the container. While the stream is spinning, the liquid and solids are forced to the outside of the container, and the air molecules, which are far less dense than the liquid or solids, are forced toward the center of the container. The air is vented or pumped out of the top of the container, and the liquid and solids drain out the bottom under the influence of gravity or may be pumped out. The ideal shape for a cyclone separator is tall and thin, so that the stream makes several passes around the circumference of the container before it exits. Virtually all standard hydrocyclone designs are tall and thin. The input stream enters at the top of a cylindrical structure with a conical bottom, and drains out the bottom of the cone. There are no internal features inside the container in a standard hydrocyclone design.
Note that the fundamental principle at work in a cyclone separator is that gases “rise” in a liquid, much like bubbles float to the top of a lake. For a cyclone separator, the acceleration imparted by the container wall has the same effect as gravity in a lake, and any air bubbles will “float” toward the center of the container.
Hydrocyclone designs have become standardized over the years. Each design may be scaled up or down, and predictions of performance versus changes in input variables are performed fairly readily for such scaled versions of the well-documented designs. A common design is the Stairmand design (see “The Design And Performance Of Cyclone Separators,” Trans. I. Chem. E., 29, 356-383), in which the top-to-bottom height of the hydrocyclone container is four times its diameter. Another common design is the Rietema design (see Chem. Eng. Sci. 1961, 15, 198-325), in which the top-to-bottom height is five times the diameter of the container.
Unfortunately, the height required by a cyclone separator may be its biggest drawback for certain applications. For example, a truck that cleans airport or aircraft carrier runways may be required to drive underneath airplane wings, thereby limiting the maximum height of the truck and all of its cleaning subsystems. Or, a truck that cleans parking garages may be limited by the clearance of each story of the garage. A typical cyclone separator might require 1 meter of vertical space, which could raise the vehicle height by 1.5 meters. On an aircraft carrier, for example, the vehicle would be too tall to pass under the wings of an aircraft, making its use impractical.
This invention relates to a method and apparatus for demisting a gaseous stream, and more particularly to the separation of moisture and solid materials from gaseous streams through use of a demisting chamber with dimensions significantly smaller than a comparable cyclone separator.